1. Field of the Invention
The present invention relates in general to a locking system for vehicle doors and particularly to an automotive door locking system of the type having an antitheft deadlock or security mechanism.
2. Description of the Prior Art
A known door locking system is provided with an antitheft deadlock or security mechanism adapted to hold a locking lever, which is movable between a locking position and an unlocking position for locking and unlocking a locking mechanism, in the locking position and prevent movement of the locking lever out of the locking position when the locking mechanism has been locked by a lock cylinder which is operated from the outside of the doer with a key. Insofar as the security mechanism holds the locking lever in the locking position, the locking mechanism cannot be unlocked by a locking button which is operated from the inside of the door. By this, it is intended to attain an improved antitheft effect since the locking mechanism cannot be unlocked even when an access to the locking button is attained by a breaking of a door glass. A door locking system having such a locking lever is disclosed in GB 2,034,802.
When the locking mechanism is to be unlocked, an unlocking switch is operated to make the security mechanism unlock the locking lever, prior to an operation of the lock cylinder for unlocking the locking mechanism.
A problem of the prior art door locking system of the above described kind is that unlocking of the locking mechanism requires a troublesome operation since an addition operation of an unlocking switch for unlocking the security mechanism is necessary prior to an unlocking operation of the lock cylinder.